An optical fiber that includes methacrylic resin such as polymethyl methacrylate or the like as a core portion has been known in the past. Such plastic optical fiber has a variety of advantage such as good flexibility, light weight and good processability, and that is easy to manufacture as a large core diameter fiber and allows to manufacture at low cost.
Generally, a halogen-containing alkyl(meth)acrylate resin with few carbon-hydrogen bonds exhibiting light absorption in the near-infrared to infrared range (600 to 1550 nm) should theoretically exhibit superior transparency.
For example, the absorption loss due to carbon-hydrogen bonds in polymethyl methacrylate at a wavelength of 650 nm is estimated at 96 dB/km. In contrast, the absorption loss due to carbon-hydrogen bonds in polymethyl α-chloroacrylate is estimated at 62 dB/km. It has been proposed to obtain a plastic optical fiber with superior thermal resistance and humidity resistance by use of a configuration in which the component forming the core portion polymer includes methyl α-chloroacrylate as a main component, one component is a halogen-containing alkyl(meth)acrylate, and a polymer having a diffractive index that is lower than the core portion forms the cladding portion (for example, Japanese Patent Application Laid-Open No. 62-147404).
Furthermore, the absorption loss due to carbon-hydrogen bonds in polytrichloroethyl methacrylate is estimated at 49 dB/km.
However, when an optical fiber is actually configured having a main component of poly trichloroethyl methacrylate in both of the core portion and the cladding portion, the problem arises that flexibility is extremely poor and use in relation to communication applications is not possible.